4. money is ...
organized in national currencies
issued by authorities (do we trust them?)
tied to political trends
exchanged directly only if cash
exchanged by intermediare in all other cases
5. money should ...
be durable
be storable in a safe say
be minted in a fair way
have a stable value during time
6. Bitcoin ...
is a digital asset
has a value based on trust
has a counter value in traditional currency
is not controlled by any authority (trustless
control)
7. Unique features
● Only “no-intermediated*” payment that can
occur remotely
● Transactions are irreversible
(*)Thousands of intermediaries = no
intermediaries
14. Timeline ...
2012 - Coinbase
2012 - BoostVC for Bitcoin startups
2012 - Bitcoin foundation
2012 - Wordpress accepts i Bitcoin
2013 - 1 BTC = 100$
15. Timeline ...
2013 - Bitcoin ATM San Diego
2013- Coinbase 5M$ funding
2013 - FBI “closes” Silk Road
2013 - Nov: 1BTC>1200$
2013 - China declares BTC is illegal
2014 - few people jailed for money laundering
16. How to receive Bitcoins
Generate a Bitcoin address
One address --> 2 keys
Private key is to spend
Public key is to receive
Keys are managed by a Wallet
18. How to spend a coin
Use the private key to sign a transaction
Send the transaction in the p2p net
...and then ...
19. Blockchain
Immutable, append only database of all
transactions copied and synced in all peers
Transaction are grouped in blocks.
Blocks are appended in avg every 10’
21. Who appends on the Blockchain
every 10’ (avg time) someone solves a
cryptopuzzle named proof-of-work with
generate the next valid block to be appended
Who solve the puzzle is also minting new
money (25BTC)
22. Mining
● New tx are broadcast to all nodes.
● Each node collects new tx. into a block.
● If proof-of-work, it broadcasts the block
● Nodes accept the block only if all tx in it are valid.
● Nodes express acceptance using the hash of the
accepted block as the “previous hash” for next block.
24. Es. proof-of-work
Es. Given A + nonce
find nonce which generate one hash starting
with 10 zeros
hash(A+nonce) =0000000000345872342642....
BRUTE FORCE!!
25. proof-of-work?
You are allowed to append a new block if you
do a given amount of work
In principle you can do a try with a pencil and
succeed
In practice the more computing power you
have the more prob. to succeed
26. Mining ... minting
In avg every 10’, the whole network succeed
in generating the block
The more are the participants the more the
puzzle is difficult (20 zeros instead of 10)
27. Mining
So, I turn on my PC, run the
software and I can mine new
money?
34. Operations in Blockchain
5pm block A closed in China
5pm block B closed in Italy
blocco blocco blocco blocco blocco A
Blockchain propagated from Cina
blocco blocco blocco blocco blocco B
Blockchain propogated from Italy
36. Biforcation
Some select A as new head
blocco blocco blocco
blocco A
blocco B
Some others select B
blocco blocco blocco
blocco blocco
37. Biforcation
The protocol says “the longest survive, the
other must be pruned”
block block block
orphan A
block B block block block
orphan orphan
38. 51% attack
Who controls 51% of total hashing rate could:
-revoke a payment (double spend)
-hinder someone else payments
Also democracy is vulnerable to 51% attack
39. Scalability
Bitcoin blockchain is more than 30GB file and
must be synced among 6000+ nodes
solutions:
pruning all data related to address with zero
balance
less blocks with more tx
46. Anonymous? No, pseudonymous
A bitcoin transaction is as anonymous as
exchanging notes in a crowded square wearing
a mask. Someone could recognize us
54. R.I.P
Think about your testament
Your bitcoins can be lost forever if you don't have a backup
plan for your peers and family. If the location of your wallets
or your passwords are not known by anyone when you are
gone, there is no hope that your funds will ever be
recovered. Taking a bit of time on these matters can make
a huge difference.
(from Bitcoin.org)